Viscometers of the type disclosed in U.S. Pat. No. 4,448,061 (May 15, 1984) of David A. Brookfield, of common assignment with the present invention, drive a cup within a housing with a liquid between the cup and the housing whose viscosity is to be measured. The liquid's viscosity retards the movement of the cup. In such viscometers a resilient connection is included in the shaft driving the cup. The deflection of this resilient connection is a measure of the drag provided by the liquid's viscosity, and the deflection is measured and may be calibrated to read the viscosity directly, see the above referenced U.S. patent and the referenced therein.
A liquid between two surfaces will shear when one surface moves relative to the other. The force needed to make such a movement is directly related to the viscosity of the liquid (with the mechanical configuration factored out). Viscometers typically rotate a cup or bob within a cylinder with the liquid therebetween, or rotate a cone relative to a plate with the liquid therebetween. In such examples, torque is directly related to the viscosity of the liquid (again with mechanical configuration factored out). The present state of the art, besides measuring torque, also includes measuring time to torque, either of which may be calibrated to read viscosity.
It is known in the art to provide a spring connection between two slotted wheels, where one wheel is attached to a mechanism that is sensitive to the drag caused by a viscous liquid, and the other wheel is attached to a mechanical drive assembly. When operated, the wheel sensitive to drag deflects with respect to the driven wheel. Optical sensors detect the slots and the resulting deflection is measured as a time delay offset between the reading of the optical sensors that is calibrated to indicate the viscosity of the liquid.
It is an object of the present invention to provide a rugged, portable viscometer with integrated electronics.
It is another object to provide a viscometer package within a housing that is explosion proof.
It is another object to provide a viscometer that operates with a wide range of liquids and over a wide range of temperatures and environments.
It is another object of the invention to provide a viscometer that is inexpensive to manufacture yet meets industry standards of accuracy, reliability, durability, dependability, and ease of maintenance and cleaning.